1. Field of the Invention
The present invention relates to a review station and an appearance inspection device for inspecting defects in semiconductor wafers.
2. Description of the Related Art
In a conventional review station for semiconductor wafers, the wafer is placed on a chuck on the X-Y stage which is moved in the X-direction and in the Y-direction according to coordinates of defective positions obtained by an appearance inspection device, and the defects are brought into a visual field of a microscope secured to an upper part of the station over the stage to review the defects.
It is, however, a recent trend to increase the size of the wafer in order to enhance the production efficiency by producing an increased number of semiconductor chips from a single wafer. Nowadays, wafers of a size in excess of 12 inches (about 300 mm) have been supplied. To observe the whole surface of the wafer 1 by moving the conventional X-Y stage in the X-direction and Y-direction only as shown in FIG. 3, however, requires a wafer-moving region (A), described by a circle of a radius of 300 mm with the objective of a microscope 2 as a center, when a wafer of a size of 12 inches is to be handled. The size of the stage unit becomes not smaller than 600 mm in the direction of depth and in the lateral direction, respectively, causing the whole device to become very bulky. Besides, the axes of the X-Y stages must cover a moving range at least equal to the diameter (D) of the wafer. Therefore, the stage must have an increased rigidity with an increase in the diameter of the wafer.
Even in the case of an appearance inspection device in which the wafer placed on the X-Y stage is continuously scanned in the X-direction by an image pick-up unit of a combination of an optical microscope and an imaging element such as a TDI while moving the position of the wafer in the Y-direction by the width of scanning, and the obtained image is successively compared among the dies to inspect defects in the wafer, it is required to provide a range for moving the X-Y stage as for the above-mentioned review station and, besides, precision of the stage decreases with an increase in the moving distance. Moreover, the stage in the appearance inspection device requires precision of a level much higher than that of the precision required for the review station, driving up the cost in proportion to an increase in the diameter of the wafer.
As described above, it is becoming more difficult to cope with an increase in the diameter of the wafer as an extension of the prior art.
The present invention was accomplished in view of the problems inherent in the above-mentioned prior art, and its object is to provide a review station and an appearance inspection device for checking semiconductor wafers without increasing the size of the whole inspection device despite an increase in the diameter of the semiconductor wafer, suppressing the moving range of the stage to be not larger than the radius of the wafer in at least one axis, and suppressing a drop in the precision of the stage.
A review station according to an embodiment of the present invention has a wafer chuck that is allowed to turn by at least 270 degrees and an X-Y stage which moves over a distance one-half the diameter of the semiconductor wafer, wherein the regions obtained by dividing the surface of the semiconductor wafer into four areas are successively observed to review the defects on the whole surface of the wafer, and the mechanism needs to move the X-Y stage only over a distance equal to the radius of the wafer compared with the moving distance of the conventional device, making it possible to decrease the size of the device as a whole. Furthermore, the moving amount of the stage is halved and the precision of the stage is highly enhanced.
According to the review station of the present invention, furthermore, the regions obtained by dividing the surface of the semiconductor wafer into two areas are successively observed to review the defects on the whole surface of the wafer.
An appearance inspection device according to another embodiment of the present invention has a wafer chuck allowed to turn by at least 180 degrees, an X-stage which moves over a distance at least equal to the diameter of the wafer, and a Y-stage which moves over a distance at least one-half the diameter of the wafer, wherein the semiconductor wafer is scanned as two half circles, and the lateral width is decreased by an amount equal to the reduction of the moving distance of the Y-stage by half.